1. Field of the Invention
The present invention relates to an endoscope system for extracting blood vessels of an object of interest from an image signal obtained by imaging the object of interest, a processor device, and a method for operating an endoscope system.
2. Description Related to the Prior Art
In medical fields, diagnoses using endoscope systems are widely performed. The endoscope system comprises a light source device, an endoscope system, and a processor device. To perform diagnostic endoscopy using the endoscope system, an insertion section of the endoscope is inserted into a body cavity and illumination light is applied to an object of interest (hereinafter referred to as the object) through a distal portion of the insertion section. An image sensor provided in the distal portion captures an image of the object irradiated with the illumination light and generates image signals. An image of the object is produced from the image signals, and displayed on a monitor.
The shape and the distribution of blood vessels are important in diagnoses using the endoscope system. The endoscope systems that extract the blood vessels from the image signals through various methods have been known recently. For example, an endoscope system that extracts the blood vessels through pattern matching has been known (see US2012/0190922 (corresponding to Japanese Pat. No. 05435746) and Japanese Patent Unexamined Publication No. 2013-255808). Also, methods for extracting blood vessels with the use of a Gabor filter, a neural network, or the like have been known (see An Automated Tracking Approach for Extraction of Retinal Vasculature in Fundus Images, A. Osareh et al., J Ophthalmic Vis Res 2010; 5(1): 20-26).
Recently, it has been known that information (e.g. the density of blood vessels or the like) that is obtained based on the correct measurement of both the position and the size of the blood vessels, in addition to the detection of the presence or absence of the blood vessels, is useful for staging of a disease (e.g. the staging of cancer or the like). For example, it has been known that the blood vessel density increases with the progression of the superficial cancer of digestive tract such as Barrett's adenocarcinoma. For this reason, it has been considered that the staging accuracy is improved by using the blood vessel density. A conventional method for extracting blood vessels with an endoscope system may extract the position of the blood vessels accurately but cannot provide correct widths of the blood vessels. Therefore the conventional method cannot correctly calculate the information such as the blood vessel density or the like.